Bottom Line:
These dramatic losses result from reduced paddy yield and increased percentages of chalky and broken kernels, which together decrease the quantity and market value of milled rice.Recently published estimates show paddy yield reductions of up to 10% across the major rice-producing regions of South and Southeast Asia due to rising temperatures.The results of our study suggest that the often-cited 10% figure underestimates the economic implications of climate change for rice producers, thus potentially threatening future food security for global rice producers and consumers.

Affiliation: Department of Agricultural Economics and Agribusiness, University of Arkansas, Fayetteville, Arkansas, United States of America.

ABSTRACTFuture increases in global surface temperature threaten those worldwide who depend on rice production for their livelihoods and food security. Past analyses of high-temperature stress on rice production have focused on paddy yield and have failed to account for the detrimental impact of high temperatures on milling quality outcomes, which ultimately determine edible (marketable) rice yield and market value. Using genotype specific rice yield and milling quality data on six common rice varieties from Arkansas, USA, combined with on-site, half-hourly and daily temperature observations, we show a nonlinear effect of high-temperature stress exposure on yield and milling quality. A 1 °C increase in average growing season temperature reduces paddy yield by 6.2%, total milled rice yield by 7.1% to 8.0%, head rice yield by 9.0% to 13.8%, and total milling revenue by 8.1% to 11.0%, across genotypes. Our results indicate that failure to account for changes in milling quality leads to understatement of the impacts of high temperatures on rice production outcomes. These dramatic losses result from reduced paddy yield and increased percentages of chalky and broken kernels, which together decrease the quantity and market value of milled rice. Recently published estimates show paddy yield reductions of up to 10% across the major rice-producing regions of South and Southeast Asia due to rising temperatures. The results of our study suggest that the often-cited 10% figure underestimates the economic implications of climate change for rice producers, thus potentially threatening future food security for global rice producers and consumers.

pone-0072157-g004: Changes in paddy and milling yield, and milling revenue across 1°C, 2°C, and 4°C increases in average growing-season temperature.The consequences of stopping the analysis at the paddy yield level are depicted above. Milling revenue lossses are greater for long-grain cultivars than medium-grain cultivars because high-temperature exposure causes much larger declines in HRY among long-grain cultivars. Medium grains are also less susceptible to chalk formation under heat-stressed conditions, but this disparity contributes relatively less to the disproportional response of milling revenue.

Mentions:
Total milling revenues across cultivars do not follow the same pattern as milled rice quantity because the quantities of broken and chalky kernels are valued less than the quantities of non-chalky kernels. Using the average U.S. FOB price for long- and medium-grain milled head rice and the average price for broken rice over the sample period, the total revenue estimates in Figure 3 illustrate the widening gap as hotter temperatures lead to quality reductions which further devalue the reduced quantity of paddy rice. Wells and XL723 illustrate this dynamic among long grain genotypes with 1°C and 2°C increases in average growing season temperature reducing paddy yield by 6.2% and 13.5%. Total milling output per hectare given these temperature increases declines by 7.6% and 16.2% in Wells and by 8% and 17% in XL723, respectively. These total quantity decreases do not illustrate the result that Wells is more susceptible to breaking during milling than XL723 (Fig. 3). The percentage changes in revenue per hectare, however, illustrate this point because we have discounted the price of broken and chalky kernels according to observed market outcomes. Cypress’s high milling yield and quality results in a relatively large percentage of revenue being derived from non-chalky head rice, but the paddy yield disadvantage leads to lower total revenue in all but the +4°C scenario, wherein the hybrid (XL723), in spite of a paddy yield advantage, records lower total revenue than Cypress. The percentage changes in paddy and milled rice yield and milling revenue presented in Fig. 4 illustrate the benefits of estimating paddy yield and milling quality responses to high-temperature stress. Across medium- and long-grain cultivars, the results show that paddy yield changes due to high-temperature stress understate the actual implications of a hotter growing season. For long- and medium-grain varieties, increasing average growing-season temperature by 1°C decreases milling revenue on average by 10% and 8%, respectively (Fig. 4). The small proportions of chalky and broken kernels in medium-grain relative to long-grain varieties (Fig. 3) cause these results.

pone-0072157-g004: Changes in paddy and milling yield, and milling revenue across 1°C, 2°C, and 4°C increases in average growing-season temperature.The consequences of stopping the analysis at the paddy yield level are depicted above. Milling revenue lossses are greater for long-grain cultivars than medium-grain cultivars because high-temperature exposure causes much larger declines in HRY among long-grain cultivars. Medium grains are also less susceptible to chalk formation under heat-stressed conditions, but this disparity contributes relatively less to the disproportional response of milling revenue.

Mentions:
Total milling revenues across cultivars do not follow the same pattern as milled rice quantity because the quantities of broken and chalky kernels are valued less than the quantities of non-chalky kernels. Using the average U.S. FOB price for long- and medium-grain milled head rice and the average price for broken rice over the sample period, the total revenue estimates in Figure 3 illustrate the widening gap as hotter temperatures lead to quality reductions which further devalue the reduced quantity of paddy rice. Wells and XL723 illustrate this dynamic among long grain genotypes with 1°C and 2°C increases in average growing season temperature reducing paddy yield by 6.2% and 13.5%. Total milling output per hectare given these temperature increases declines by 7.6% and 16.2% in Wells and by 8% and 17% in XL723, respectively. These total quantity decreases do not illustrate the result that Wells is more susceptible to breaking during milling than XL723 (Fig. 3). The percentage changes in revenue per hectare, however, illustrate this point because we have discounted the price of broken and chalky kernels according to observed market outcomes. Cypress’s high milling yield and quality results in a relatively large percentage of revenue being derived from non-chalky head rice, but the paddy yield disadvantage leads to lower total revenue in all but the +4°C scenario, wherein the hybrid (XL723), in spite of a paddy yield advantage, records lower total revenue than Cypress. The percentage changes in paddy and milled rice yield and milling revenue presented in Fig. 4 illustrate the benefits of estimating paddy yield and milling quality responses to high-temperature stress. Across medium- and long-grain cultivars, the results show that paddy yield changes due to high-temperature stress understate the actual implications of a hotter growing season. For long- and medium-grain varieties, increasing average growing-season temperature by 1°C decreases milling revenue on average by 10% and 8%, respectively (Fig. 4). The small proportions of chalky and broken kernels in medium-grain relative to long-grain varieties (Fig. 3) cause these results.

Bottom Line:
These dramatic losses result from reduced paddy yield and increased percentages of chalky and broken kernels, which together decrease the quantity and market value of milled rice.Recently published estimates show paddy yield reductions of up to 10% across the major rice-producing regions of South and Southeast Asia due to rising temperatures.The results of our study suggest that the often-cited 10% figure underestimates the economic implications of climate change for rice producers, thus potentially threatening future food security for global rice producers and consumers.

Affiliation:
Department of Agricultural Economics and Agribusiness, University of Arkansas, Fayetteville, Arkansas, United States of America.

ABSTRACTFuture increases in global surface temperature threaten those worldwide who depend on rice production for their livelihoods and food security. Past analyses of high-temperature stress on rice production have focused on paddy yield and have failed to account for the detrimental impact of high temperatures on milling quality outcomes, which ultimately determine edible (marketable) rice yield and market value. Using genotype specific rice yield and milling quality data on six common rice varieties from Arkansas, USA, combined with on-site, half-hourly and daily temperature observations, we show a nonlinear effect of high-temperature stress exposure on yield and milling quality. A 1 °C increase in average growing season temperature reduces paddy yield by 6.2%, total milled rice yield by 7.1% to 8.0%, head rice yield by 9.0% to 13.8%, and total milling revenue by 8.1% to 11.0%, across genotypes. Our results indicate that failure to account for changes in milling quality leads to understatement of the impacts of high temperatures on rice production outcomes. These dramatic losses result from reduced paddy yield and increased percentages of chalky and broken kernels, which together decrease the quantity and market value of milled rice. Recently published estimates show paddy yield reductions of up to 10% across the major rice-producing regions of South and Southeast Asia due to rising temperatures. The results of our study suggest that the often-cited 10% figure underestimates the economic implications of climate change for rice producers, thus potentially threatening future food security for global rice producers and consumers.